ER ee eg Oe ES HO TN ET, RNR gi SY Ms Oe LL Sete SER Ge ER Gere een A Se eR ag OAS Eee ANE ye ates ORE = A ee eS eee RM 
Bak Saree hE poet peer . : aoe aries Sie E 
W. Ferrel—Cyclones, Tornadoes and Waterspouts. 47 
into the central part of the tornado, where the ascending 
currents are strong enough to carry them up again into the 
region of soft snow mixed with rain, where they receive 
the center again, to commence another similar revolution. 
While in the upper snow region it receives a coat of snow, 
and while in the region of cloud and rain, a coat of solid 
ice. Hence it is no unusual chines to find large hail-stones 
composed of a number of coatings like an onion, these coat- 
ings ponsieting of alternate layers of frozen soft snow and 
solid ice.* 
Sand-spouts.—These occur mostly on dry, sandy deserts 
where the surface becomes very much heated, and the rate of 
decrease of temperature with increase of altitude is such that the 
unsaturated and sete rope dry air is in the state of unsta- 
sides, in toward the acre part, and thus the nae part of 
the air assumes the figure of a column. 
As the particles of sand gyrate rapidly with the air, the centri- 
fugal force of the gyrations tends to driye the Lobia from 
the center, but this is counteracted by the resistance e 
indrawing currents, which is a function of the size of she’ parti- 
cle and the strength of their currents, since it is nearly as the 
square of the product of the velocity of the current into the 
diameter of the particle. Hence, particles of sand of different 
sizes arrange themselves at different distances from the center, 
the smaller particles penetrating nearer the center, since the 
centrifugal force is as the cube of the diameter, while the resist- 
ence of the inflowing current is nearly a s the square of the 
diameter. If, however, the particle were city large, it might 
* See American Journal of Science, I, vol. 1, p. 403. 
